This invention relates to bone cements in general, and more particularly to systems and methods for preparing bone cements from a solid component and a liquid component by mixing the two components in a vacuum.
In many orthopaedic surgical procedures, bone cements are used to fix implants to bone. These bone cements are generally polymeric and/or copolymeric materials which are prepared by polymerizing the cement""s constituent components as the cement is needed during the surgical procedure. More particularly, such bone cements are typically prepared by polymerizing a liquid monomer and a powdered polymer and/or copolymer, e.g. polymethyl methacrylate (xe2x80x9cPMMAxe2x80x9d) and/or a polystyrene copolymer.
Unfortunately, it has been found that as the cement""s constituent components are mixed together to effect the aforementioned polymerization, air bubbles are generally introduced into the cement. The presence of these air bubbles increases the porosity of the cement and thereby undermines its structural integrity. Conversely, it has also been found that the strength of the cement can be significantly increased if the air bubbles are eliminated from the mixture.
On account of the foregoing, bone cements of the sort described above are preferably prepared by mixing the constituent components in a vacuum.
Unfortunately, prior art systems and methods for mixing bone cement in a vacuum in an operating room environment have not proven to be particularly convenient to use. Among other things, such prior art systems and methods generally require operating room personnel to transfer the bone cement""s powdered polymer and/or copolymer component into a mixing bowl from its shipping container, and then to transfer the bone cement""s liquid monomer component from its shipping container into the same mixing container prior to establishing a vacuum in the mixing bowl and then effecting mixing.
Accordingly, one object of the present invention is to provide an improved system for mixing bone cement.
And another object of the present invention is to provide more convenient system for mixing bone cement in a vacuum in an operating room environment.
Still another object of the present invention is to provide an improved method for mixing bone cement.
Yet another object of the present invention is to provide more convenient method for mixing bone cement in a vacuum in a operating room environment.
These and other objects of the present invention are achieved through the provision and use of a novel system and method for mixing bone cement.
The novel system for mixing bone cement generally comprises (i) a container within which the constituent components of the bone cement are mixed under vacuum; (ii) a vacuum pump for pulling a vacuum; (iii) a vacuum line interconnecting the vacuum pump and the container; (iv) a check valve disposed in the vacuum line for maintaining a vacuum pulled in the container by the vacuum pump; (v) a vacuum indicator disposed in the vacuum line for indicating when a predetermined level of vacuum has been attained in the container; and (vi) a filter disposed in the vacuum line for preventing unwanted materials (e.g., powdered polymer and/or copolymer, liquid monomer, and/or mixed cement) from passing from the container to the check valve and/or vacuum pump.
In accordance with the present invention, the bone cement""s powdered polymer and/or copolymer component is pre-packaged in the aforementioned container, and the bone cement""s liquid monomer component is pre-packaged in a separate holder.
In one form of the invention, the container can comprise a sealed cartridge for a cement dispenser, or a sealed mixing bowl or other vessel. The container comprises an injection port for connection to the holder containing the bone cement""s liquid monomer component, an exhaust port for connection to the vacuum line and hence the vacuum pump, and an agitator having a mixing paddle disposed inside the sealed container and an actuating handle disposed outside the sealed container, with a shaft connecting the mixing paddle to the handle. Barrier means are disposed inside the container, between the contents of the container and the exhaust port. These barrier means comprise a plurality of indirect pathways which permit gas to pass out of the container via the exhaust port but prevent solid and/or liquid material from passing out of the container via the exhaust port. Preferably, an absorbent filter is disposed in the exhaust port, downstream from the barrier means but upstream from the vacuum line, to trap any solid and/or liquid material which might pass by the barrier means.
In another form of the invention, the container comprises sealed cartridge for a cement dispenser. This cartridge comprises an exhaust port for connection to the vacuum line and hence the vacuum pump, an agitator having a mixing paddle disposed inside the sealed cartridge and an actuating handle disposed outside the sealed cartridge, with a hollow shaft connecting the mixing paddle to the handle, and an injection port for connection to the holder containing the bone cement""s liquid monomer component. In this form of the invention, the injects port is disposed in the handle of the agitator and communicates with the interior of the sealed container through the agitator""s hollow handle. A porous plug closes off the distal end of the hollow handle, whereby liquid monomer can pass from the injection port through to the interior of the sealed container but powdered polymer and/or copolymer and/or mixed cement will be prevented from passing out of the sealed container through the agitator during cement mixing. Preferably the agitator""s shaft is formed out of a thin-walled exterior tube and a resilient interior tube, with the thin-walled exterior tube including a breakaway notch, and with the distal end of the resilient interior tube being connected to the porous plug, whereby, at the conclusion of cement mixing, the handle of the agitator can be retracted relative to the container, the thin-walled exterior tube can be broken off at the breakaway notch, and the resilient interior tube can be used to withdraw the porous plug from the remaining stub of the thin-walled exterior tube, whereby the stub of the thin-walled exterior tube can become an ejection port for the sealed cartridge.
In still another form of the invention, the container can comprise a sealed cartridge for a cement dispenser, or a sealed mixing bowl or other vessel. In this form of the invention, the holder containing the bone cement""s monomer component comprise glass ampoule having an easily fractured neck at one end. The container comprises an injection port for connection (through intervening elements) to the monomer ampoule, an exhaust port connection to the vacuum line and hence the vacuum pump, and an agitator having a mixing paddle disposed inside the sealed container and an actuating handle disposed outside the sealed container, with a shaft connecting the mixing paddle to the handle. The monomer ampoule is disposed in an ampoule breaker/injector device which is connected to the container""s injection port. The apparatus is arranged so that when a vacuum is drawn in the sealed container, the monomer ampoule will be automatically broken at its easily fractured neck by forces generated by the vacuum and the liquid monomer will then be draw down into the sealed container through the container""s injection port.